Overall, the concept is really good and the art is simple but works. I think switching between using your reactor to mine and cooling it works well and makes sense - but the execution is a little frustrating. The problem is that both phases are similar times, and not only is your rover very slow at first, you cant do much in the cooling phase except upgrade - and you can only afford things after mining. Giving the player more time on mining, allowing you to "save" up" energy or having something to do while on "cool-down" would probably fix it.